| kinser |
Hi all,
Long time no post....
I am planning on building a GC with OPA541 or OPA549, and i think im going to go with the 549 from what people here have said.. its got more power and sounds better... BUT it max V+/- is 30Vdc.. and i have a 25-0-25 260va EI trafo.. how should I lower the voltage from 35vdc+/- to about 25-28vdc+/-? would 1 pair of LM317/337 do the job?
Thanks,
Kinser |
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| lgreen |
| That should work. Make sure you get good heat sinking on those regulators. |
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| kinser |
lgreen,
Thanks for the help... forgot to mention.. its a stereo amp.. so a pair of the LM317/337 will do with heatsinks, with 2 549's?
Thanks,
Kinser |
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| kinser |
tobias_svensk,
Thanks for that.. had a look at it befor.. would rather not use it... becuase i want to keep this amp as small and simple as possible..can i use LM338 with both positive and negative rails? or does it have another chip to go with it?(eg, LM338 for positive rail, LMxxx for negative rail)
Thaks,
Kinser |
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| tobias_svensk |
Two LM338 will work if you connect them as in the picture.
You could always put some smaller caps in the LM338 supply to keep down the size. Because the LM338 & LM317 is the same size anyways.
And driving a stereo amp with one LM317 plus one LM337? i can't see that coming.
You could try an unregulated psu, just do a simple CRC or CRCR or whatever is popular :) |
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| kinser |
So,
What I should do is make 2 LM338 circuits.. connect 1 normal.. to the positive rail.. and then with the 2nd ciruit i connect the "In" to the center tap/ground, and the com/ground to the negative rail? like in the ciruit using the 338's? but the circuit will be with smaller/less components...
Does this all make sense to you? and is it the way to do it?
Thanks,
Kinser |
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| Upupa Epops |
| Hi Kinser, don't make it crazy, use OPA 541, which have higher voltage ( +/- 40 V ), but it is old circuit, with nonextraordinary parametres ;), better is to use some LM... circuit. |
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| kinser |
Upupa Epops,
Thank you! I will go with 541's.. much more simple.. although i really want to us 549's.. if i had some LM's i would use em'.. but i have none left.. they were sample from national.. and they are not cheap here.. at least not cheap for me...the are cheap for big companys and repair-men...
BTW.. Im only 14 years old... heheh
Thanks Alot!! :-)
Kinser.. will show you resalts in a couple of days! |
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| Upupa Epops |
| Don't drink so much Cola's and money will be no problem ;) . Good luck. |
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| tobias_svensk |
Hehe
National have never sent me any samples :xeye: |
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| Upupa Epops |
| Maybe guys from NS knows, that in Sweden don't live poor people :xeye: . |
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| tobias_svensk |
| Maybe so, but i'm not in that category :) |
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| Upupa Epops |
| Tobias, Mundorf caps aren't free :D . |
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| tobias_svensk |
| Heh what? :) |
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| kinser |
Hey again,
I have 2 q's...
1.this might be kind of off topic - does anyone have a simple loudspeaker protection circuit?
2. I am helping my friend build a 4 channel amp with opa549's..a chip per channel. and he has a big 550va EI trafo.. with 22-0-22.. thats about 31vdc+/-.. and 549's are 30vdc+/- max.. so can i run 4 of them off 1 trafo.. with rail voltage of 31vdc+/-? wont there be any voltage loss on the rails with 4 chips?
Thanks,
Kinser |
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| kinser |
DT,
Thanks! have seen that one befor but dont know were... i will make it for the OPA541's! Thanks again.
Does any one elso have an answer for my second Q?
Thanks,
Kinser |
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| boholm |
Ad. 2:
You are just over the limit - just. If you dare you could try and use it. No garantees, but it might work.
Furthermore, if the transformer is not loaded it gives out higher voltage than rated. If I were you I would find out how big a load your 4 amps are (no signal) with a smaller transformer, and then calculate a resistor as test load on the wanted transformer, and then see how big a voltage it gives. Or as a pointer; test with a 2Kohm resistor.
Using one diode bridge per voltage side will help, but is it enough? |
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| kinser |
Hi Again,
I have started to build the LS protection circuit, and i saw somthing stange in the circuit:
The "-" leads of both 47uF caps and connected, and 1 "+" lead is connected to ground, and the 2nd "+" lead is connected to 22k resistors....
Is this right, or is it a mistake that wasn't noticed?
Here is the like to the schematic: http://www.astro.uu.se/~marcus/private/dcprot.jpg
Thanks,
Kinser |
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| kinser |
Anyone?
Pleaseee...:bawling: :bawling: :bawling:
I really want to finish this so that i can start on the amps..
Thanks,
Kinser |
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| boholm |
Patience, my friend. All good thing comes to he, who waits ;-)
The two capacitors are correct connected - making two electrolytics into a bipolar one. |
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| slackman |
| Yep, you can replace these two elkos with a 22uF bipolar elko - the two-elko-version is much cheaper... ;) |
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| kinser |
Hey,
Thanks you to both boholm and to slackman!
Now all I need is to find a TIP121 transistor.. are there any substitutes for the TIP121 transistor? becuase if there are i may have one at home... if there is not any then I will have to go buy... So... is there a substitute?
Thanks,
Kinser |
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| boholm |
| With 12 volts only and the need to drive only a relay I would say that any npn darlington transistor (> 2W) will do. It is the relay that will determine the power needs. A TIP121 IMHO may be a bit overkill as regard to the relays I know of. They seldom use more than 50 mA. But then again I do not know what kind of relay you have or will use. |
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